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Advances in Applied Science Research, 2012, 3 (1):95-102
ISSN: 0976-8610
CODEN (USA): AASRFC
Beach Rocks from the South East Coast of Tamilnadu, India:
A Spectroscopic Study
R. Ravisankar1* P. Eswaran2, A. Rajalakshmi3, A. Chandrasekaran4, K. K Thillaivelavan5
and B. Dhinakaran5
1
Post Graduate and Research Department of Physics, Government Arts College, Tiruvanamalai,
Tamilnadu, India
2
Department of Physics, Vel Tech Technical University, Avadi, Chennai, Tamilndu, India
3
Department of Physics, SSN College of Engineering, Kalavakkam, Chennai, Tamilnadu, India
4
Department of Physics, Global Institute of Engineering & Technology, Vellore, Tamilnadu, India
5
Department of Physics, Government Arts College, Chidambaram, Tamilnadu, India
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ABSTRACT
Beach rock has only rarely been observed in the coasts. It is a hard costal sedimentary formations consisting of
various beach sediments, lithified through the precipitation of carbonate cements. One such formation is noted on
the South East Coast of Tamilnadu, India. The objective of this contribution is to collect and review information on
reported occurrences, characteristics and formation mechanism of beach rocks and applying the spectroscopic
techniques for beach rock formation and evolution. The FT-IR and XRD technique is used to identify the constituent
of minerals and cementing materials of the beach rocks. The instrumental neutron activation analysis (INAA) is used
to determine the elemental geochemistry of the beach rocks. Results are discussed and the conclusions are drawn.
The combined spectroscopic techniques are used to throw light on the nature and cause of cementation.
Keywords: Beach rocks, Mineral Analysis, FT-IR, XRD, Multi-Elemental Analysis, INAA,
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INTRODUCTION
Earth’s crust is made up of various types of rocks.Large areas of the earth are covered with soil. But soil itself is a
mixture of tiny rock fragments, decayed organic matter, water and air. Rocks are the largest accumulation of
minerals cemented together and hence generally minerals constitute the crust of the earth. Some of the elements of
the earth’s crust rarely occur individually in nature, but are generally found in chemical composition with some
other elements in the form of compounds. In the earth’s crust the rocks can be classified, in general, into three types,
according to their origin viz.,(1) Igneous, (2) Metamorphic and (3) Sedimentary. Igneous rocks are formed by the
hardening of magma, i.e., molten masses rising to the surface from the entrails of the earth. Metamorphic rocks are
formed from the subjection of pre-existing rocks to intense pressure and temperature, which promotes
recrystallization and because of recrystallization new rock is produced with new texture and perhaps also with new
mineral composition. The sedimentary rocks originate from detrital material and dissolved mineral matter produced
due to decomposition of pre-exciting rocks and also from the degrading remains of plants and animals.
Beach rock comes under the classification of sedimentary rocks.Beach rock, most commonly appearing as layered
deposit inclined towards the sea, is a sedimentary formation indurated by the effects of carbonate cement-aragonite
or magnesium calcite initially-formed in the intertidal zone. Beach rock or beach sandstone consists of beach sand
cemented together by calcium carbonate to form friable to well-cemented rock. Beach rock forms most commonly
on beaches composed of calcareous shell and coral grains, but it can also develop in beaches of quartz sand or other
mineral composition.It forms best on sand beaches; shingle or conglomeratic beach rock is less abundant. The
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natural factor of the beach, such as gentle slope of the foreshore, sufficient shell content and ground water
temperature have also favoured the formation of beach rocks. Essential to beach rock development is ground water
with enough calcium to provide cementing agent. The occurrence, cementation and formation of the beach rock is
outlined below.
1.1. Occurrence
Beach rock is generally limited to tropical and subtropical climates, though not every tropical beach has beach rock
[1-3]. Beach rock has also been reported from temperate regions, but such occurrences are rare. For example,
Binkley and Wilkinson [4] describe beach rock from Ore Lake, Michigan. Furthermore, there appears to be no
connection with rainfall as beach rock has been found in arid (Arabia) and humid (Pacific and Caribbean) regions
[4-5]. Beach rock also shows no obvious preference for either a high-or low-energy beach environment [5].
The constituents of beach rock are generally similar to the surrounding unconsolidated beach material [5-9]. The
sediment is generally carbonate [7] although beach rock with constituents of volcanic origin has been reported from
Hawaii [10-11]. Purely silt-or clay-size beach rocks are not known [3].
1.2. Cementation
Beach deposits along many coasts are cemented with either aragonite or calcite. Cementation is assumed to have
occurred in situ or beneath thin sediment cover [8]. Carbonate cement is formed in the intertidal zone of the world’s
tropical and sub tropical beaches [12]. Cemented beach rock from Mediterranean [6], the Red sea [13],
Venezuela[14], and South Africa [15] has been studied and reviewed. Russell [1] reviewed several studies on beach
rocks and their cementation.
Lithification of beach rock can occur very rapidly, even within just a few years [5-6, 9, 16-17]. However, the length
of time during which precipitation occurs is not known, or whether the cement forms by slow continuous growth at
levels of moderate super saturation, or sporadically at times of favorable conditions. Although all beach rocks are
cemented by calcium carbonate [7].
Beach rock cements are commonly composed of aragonite or high-magnesian calcite or calcite, which are consistent
with carbonate precipitation in a marine or, at least, saline environment.All theories of beach rock formation have
one thing in common: cementation must take place within the intertidal zone.
1.3. Formation
Studies of the beach rock from other localities demonstrate that the usual cement in such rock is aragonite, calcite or
high magnesium calcite or all of them. The occurrence of beach rock formation is a result of direct precipitation of
calcite and/or aragonite from solution within the beach rock. Cementation occurs in two stages; an initial
cryptocrystalline high-Mg calcite rim first coats grains, followed by the growth of fibrous carbonate (generally high
Mg calcite or aragonite) commonly as isopachous coating around the framework grains. The presence of such
cementing agents in most beach rock suggests that the cement was formed in contact with seawater, whereas in fresh
water the low concentration of Mg ions favours formation of low Mg calcite [18].
The second possible water controlled driving mechanism of the aragonite-to-calcite transformation which is
freshwater-seawater mixing is as follows. The mixing of water is saturated or supersaturated with respect to
calcium carbonate at differing CO 2 pressures, temperatures to calcium carbonate and thus promotes
dissolution [19-22]. In general, beach rock occurs in tropical and subtropical beaches as layers of cemented beach
sediments and occupies a position within intertidal and low supratidal zone.
Based on the above discussion, a detailed examination is required to understand the process of cementation of the
beach rocks in the marine environment. The present work aims to identify the cementing material for the beach rock
formation using spectroscopic techniques.
MATERIALS AND METHODS
2.1. Sample collection and preparation
Beach rock samples were collected from 15 sampling sites, stretching from Rameshwaram to Kanyakumari along
the South East Coast of Tamilnadu (Fig 1). From the sampling sites, approximately 1 kg sample was taken from the
same rock and collected in a plastic bag. All the samples were brought to the laboratory, cleaned, weathered surface
removed and the remaining fresh materials crushed into small pieces. These samples are powdered using agate
mortar and dried for 24 hrs at a temperature of 110°C and then pulverized to particle sizes not greater than
2mm mesh screen.
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2.2. FT-IR Analysis:
The major and minor minerals are qualitatively determined by using FT-IR. Sample of 2 mg is mixed with 40 mg of
spectroscopic KBr in the ratio 1:20 using a mortar and pestle. The Nicolet Avator 360 series FT-IR at Annamalai
University, Annamalainagar, Tamilnadu, India was used. The FT-IR spectra were taken in 4000-400cm-1. The
instrument scanned the spectra 16 times in 1 minute and the resolution was 5cm-1. A typical FT-IR spectrum is
shown in Fig-2.
2.3. XRD Analysis:
XRD patterns of beach rock powder samples were recorded at room temperature by X-ray diffractrometer (D500,
Siemens) having a curved graphite crystal diffracted monochromator, with a source of Cu Kα ray and NaI(Tl)
scintillation detector from Material Chemistry Division, Chemical groups, Indira Gandhi Centre for Atomic
Research (IGCAR), Kalpakkam, Tamil Nadu, India. A narrow slit of 0.1mm was used with a scanning speed of 1/2°
per minute and time constant of two seconds. The diffraction patterns were obtained over the 2θ values in 20°–80°.
A typical XRD spectrum is shown in Fig-3.
2.4. INAA Analysis
2.4.1. Sample irradiation and counting
Irradiations were performed in thermal neutron flux of 1011cm-2·s-1 using pneumatic transport facility of KAMINI
research reactor, Indria Gandhi Centre for Atomic Research (IGCAR), Kalpakkam, Tamilnadu, India. With a view
to assay the short and long-lived radionuclides, two sets of irradiation, 5 min and 5 h were performed. The samples
of 5-min irradiation were counted for 100 to 300s after 10-min cooling for the determination of 28Al, 27Mg, 49Ca,
51
Ti and 52V and a cooling of 200-300 min for analyzing 165Dy, 56Mn and 24Na. The samples of 5-h irradiations to
determine the medium and long-lived radionuclides (42K, 51Cr, 59Fe, 60Co, 95Zr, 140La, 141Ce, 152Eu 153Sm, 175Yb and
181
Hf) were counted for 10,000-30,000 s after a cooling time of 2, 4 to7 and 35 to 50 days.
2.4.2. Radioactive assay
After irradiation the polypropylene tubes containing the sample and the gold as the standard for quantitative analysis
were washed under running water, wiped and mounted on standard Perspex plates. Samples were assayed for γactivity of the activation products using an 80 cm3 HPGe detector coupled to a PC based 4K analyzer in an
efficiency calibrated position with reproducible sample to detector geometry. The sample to detector distance was
maintained at 12-15 cm depending upon the level of activity to avoid true coincidences effects. The detector system
had a resolution of 1.8 keV at 1332 keV. The activities of radionuclides were considered as a function of time to
ensure purity and identity. Gamma-ray standard of 152Eu was used for efficiency calibration of the detector, at
different distances between the sample and detector in a stable source to detector geometry.
2.4.3. Calculations
Peak areas corresponding to different photo peaks, after subtracting the linear Compton background, were converted
to specific count rate (Asp) by Asp=PA /SDCW, where PA=peak area, S=saturation factor, C=counting correction,
D=decay correction, and W=weight of the sample.
The concentration of the ith element (in µg/g) was calculated by Conc=[Asp/(A*spKanal)], where Asp=specific count
rate corrected per gram of the sample, A*sp=specific count rate of 198Au, and Kanal = K0 [(f+Q0 (α))/(f+*Q
(α))]·(ξ/ξ*), where ξ is the detection efficiency of the detector for the γ-ray energy used, f is the sub-cadmium to epicadmium neutron flux ratio, and Q0(α) is the ratio of cross sections and is equal to I0(α)/σth, where I0(α) is the
infinitely dilute resonance integral corrected for the non-ideal epithermal neutron flux distribution. Validation for the
experimental setup was done by irradiating the Standard Reference Material (SRM 1646a estuarine sediment) for the
same period of time with comparator and the sample in the same location of the reactor (Table-1). The SRM
analysis agreed well with the certified values.
RESULTS AND DISCUSSION
3.1. FT-IR Analysis
The i.r.absorption peaks were compared (Table 2) with available literature, the minerals identified as quartz,
orthoclase, albite, kaolinite, montmorllinite, illite, calcite, aragonite, dolomite, ilmenite and rutile [23-25].. The large
number peaks of calcite in the i.r. spectrum indicate the abundance of calcite in the samples and it may be due to the
typical beach rock formation. Beach deposits along many coasts were cemented with either aragonite or calcite
because some of these “beach rock” derive their cement from seawater. Seawater is several times supersaturated
with respect to calcite and aragonite and also it is the source of the cementing agent calcium carbonate
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3.2. XRD analysis
Qualitative mineralogy of the beach rock samples was determined with the standard interpretation procedures of
XRD. Quartz, albite, orthoclase, kaolinite, calcite, aragonite, ilmenite, rutile and almandine garnet were identified
from the peaks in diffractrogram. Major minerals in the samples are quartz and calcite. The presence of heavy
minerals (ilmenite, garnet, rutile etc.) may be the contribution from the hinterland geology, laterization of gneissose
rocks, occurrence of small streams and categorization by waves and tides.
The qualitative identification of the minerals in beach rock samples was carried out by using FT-IR and XRD
techniques. The combined techniques reveal the presence of minerals such as quartz, orthoclase, albite, kaolinte and
montmorlinte in the samples. Beach rock is mostly composed of marine shell fragments (e.g., molluscs, coralline
algae, foraminifera) and terrigenous detritus (e.g., quartz and feldspar). The presence of quartz and feldspar in our
study indicates that they also play a role for the cementation of beach rock samples.
From the IR and XRD spectra of the samples, the peaks indicating the abundance of minerals such as carbonate
groups calcite and aragonite occupy large portion of total peak areas. The high abundance of calcite in the samples
was due to the typical beach rock formation. This is may be due to the beach deposits along many coasts were
cemented with either aragonite or calcite because some of these “beach rock” derive their cement from seawater.
Seawater is several times supersaturated with respect to calcite and aragonite and also it is the source of the
cementing agent calcium carbonate. The bulk mineralogy of beach rock samples from the IR and XRD studies
reveals that calcite, aragonite and slightly lesser extent quartz are the dominant minerals. A similar mineralogical
composition characterizes the beach rocks of other locality.
3.3. INAA Analysis:
The elemental contents in the beach rock samples are reported in Table 3. The calcium is the highest of all the
elements in almost all the samples. This is due to high abundance of calcium carbonate in tropical and subtropical
areas of ocean [26] and also typical beach rock formation [9] .The highest Al content at S13 indicates the higher
degree of weathering and reflects the degree of influence of sediment, whereas the lowest Al content at S1 implies
the finer nature of sediment containing clay minerals and iron oxides [27].
The variation in the distribution of Ca, Mg, Na and K in some locations may be mainly controlled by clay minerals
in the study area. Nelson [28] has pointed out that in the processes of ion exchange, the common ions inherited from
soil environment (Ca2+ and H+) by the absorption in surface particles are replaced by most abundant ions (Na+ and
Mg+)6. The net reaction between fluvial clays and seawater is primarily an exchange of seawater Na for bound Ca+.
The higher Na and Mg concentrations at S13 may be due to the low Ca content in the marginal environment such as
tidal channel and, swamps can also be attributed to the above replacement of Ca by other ions [29].
Table-1 Analysis of standard Reference Material by INAA
Elements
Al %
Ca %
K%
Fe %
Na %
Ti %
V
Mn
As
Cr
Measured Value Certified Value
2.40 ± 0.7
2.30 ± 0.2
0.53 ±0.4
0.52 ± 0.6
0.89 ± 0.7
0.86 ± 0.8
2.17 ± 1.4
2.08 ± 1.2
0.78 ± 0.8
0.74 ± 0.9
0.47 ± 0.7
0.46 ± 0.6
43.94 ± 0.2
44.84 ± 0.4
231.33 ± 1.2
234.50 ± 1.6
6.26 ± 0.17
6.23 ± ± 0.15
41.3 ± 0.6
40.90 ± 0.8
Ce
34.51 ± 0.7
34 ± 0.2
Co
5.6 ± 0.2
5 ± 0.3
La
20 ± 1.6
17 ± 1.2
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Fig.1.Location Map
Fig.2. A typical FT-IR spectrum of Beach rocks of South East Coast of Tamilnadu
The presence of Fe, Ti, Cr, Mn and V were indicates the minerals such as ilmenite, rutile and chromite present in the
samples as well as the study area. This may be due to heavy minerals present in the samples and also in sediments
[30].The low concentration of Co in the present study shows that its mobility is reduced in the carbonate dominant
environment [31].The presence of Zr and Hf in the study indicates the possibility of heavy minerals present in the
sediment. In beach rock samples, the contents of REEs follow the order Ce>La>Sm>Yb. This is consistent with
average abundance in the earth’s crust.
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The variation of the different trace elements in the present study may be due to the nature of weathering processes,
and the velocity of transporting media. The total trace elements concentrations in sediments depend not only on the
trace element input but also on the mineral composition of the sediment, which can be different from area to area.
Fig.3. A typical X-ray diffractrogram of Beach rock of South East Coast of Tamilnadu
Table 2: Observed Absorption Frequency in the region of 400 – 4000 cm-1
S1
1160,
795
455,
S3
455, 775, 795
S5
457, 695, 775
S7
456, 775, 795
775,
405
1035, 3660
3440
-
435
406,
585
1035, 3620
475, 3440
915
405,
1035
475, 3445
915
405,
585
1035, 3690
3445
-
435,
540
435,
540
435,
540
S9
455, 775
S11
457, 695, 775, 795
435,
540
S13
455, 795
435
S15
695, 775
435,
540
405
1035
3445
915
405
1035, 3690
3445
915
1035, 3660,
475
-
1040,
3690
3445
-
405,
585
405,
585
3660,
715, 875, 1425,
1800, 2515
715, 875, 1800,
2515
715,
875,
1795,2515
715, 875, 1425,
2515, 2875
715, 875, 2515
715, 875, 1425,
1800, 2515, 2875,
2875
715, 875, 1425,
1795
715, 875, 1425,
1800, 2515, 2875
Dolomite
Aragonite
Iltite
Kaoilinite
435,
540
Calcite
Carbonate Minerals
Montomorilinte
Clay Mineral
Albite
Orthoclase
Quartz
Sample No
Feldspar
1080, 1475
-
855, 1080
-
855, 1080, 1475,
1785
2525
1080, 1475
-
855, 1080, 1475,
1785
-
855, 1080
2525
855, 1080,
1475, 1785
2525
1085, 1785
2525
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Table 3 Elemental concentration of Beach rock samples of South East Coast of Tamilnadu (in ppm unless % indicated)
Elements S1
S2
S3
S4
S5
S6
S7
S8
S9
S10
S11
S12
S13
S14
S15
Al %
0.15 1.2
1.3
2.4 0.61 3.18
2.03
2.33 1.43 2.25 1.68 2.23 7.73 0.72 3.42
Mg %
0.70 0.88 3.04 1.13 2.63 1.32
2.55
3.20 2.20 2.27 0.73 1.22 3.21 0.70 2.48
Na %
0.42 0.57 0.43 0.52 0.39 0.85
0.59
0.15 0.51 0.44 0.43 0.96 1.79 0.22 0.52
Ca %
15.83 22.44 17.99 24.28 18.53 15.31 18.14 12.18 14.24 23.59 24.69 18.22 10.87 20.52 4.43
Ti %
0.07 1.20 0.49 ND 0.04 0.34
0.12
7.04 0.06 ND 0.52 0.38 0.30 0.16 15.66
Fe %
0.81 2.37 2.48 0.29 0.33 1.39
0.67 15.83 0.44 0.61 0.73 1.13 5.45 0.51 23.12
Co
3.91 7.07 9.58 2.99 4.99 9.06
5.5
30
7.2
2.78 3.57 3.26 14.83 6.64 45.85
Cr
14.94 26.1 53.95 ND 21.75 36.31 102.84 187 29.48 55.58 38.28 25.95 97.2 54.39 304
V
4.76 62.6 37.82 5.66 5.87 20.25 13.31 416.2 15.68 72.45 30.97 27.98 62.87 11.87 631.9
Hf
5.21 17.24 26 2.24 3.81 14.78 9.14 56.28 5.63 6.88 45.43 20.25 14.73 4.56 101.4
Zr
ND ND 2348 ND ND ND 1612.24 2662 ND 1087 1990 1525 1532 1027 4692
Mn
167.5 407.5 385.9 215.5 146.9 686.5 226.36 2809 778.84 499.4 114.1 139.8 580.3 432.2 2514
La
101.0 78.58 27.14 16.05 9.49 38.22 16.58 140 10.06 25.14 121.1 131.5 56.80 29.94 678.0
Ce
18.14 137.7 37.32 29.17 16.57 87.29 57.87 221.9 19.48 77.22 225.3 247 86.43 51.29 1288
Sm
1.10 5.62 2.49 1.64 1.05 3.08
1.22 11.05 0.95 3.80 11.06 12.33 4.07 2.43 60.36
Eu
0.49 1.06 2.21 0.74 0.80
2
0.96
2.85 0.84 0.68 1.35 1.34 2.56 0.55 5.69
Tb
0.30 0.99 0.41 0.18 0.16 0.74
0.22
1.25 0.45 0.67 0.98 1.25 2.80 0.6 7.21
Yb
0.44 0.19 0.65 0.41 0.22 0.824 0.49
2.61 0.56 0.89 1.35 2.81 4.79 1.08 14.08
S1-Rameswararm, S2-Pampan, S3-Mandapam, S4-Pudumadam, S5-Kilakarai, S6-Valinockam, S7-Surangudi, S8-Sippikulam, S9-Veerapandia
Pattanam, S10-Tiruchendur, S11-Manapad, S12-Ovari, S13-Idinthakarai, S14-Perumnal,S15-Kanyakumari. ND-Not Determined
CONCLUSION
Beach rock formation is a special type of formation when compared to other types of formation.The detailed
examination of cementing material in beach rock is analysed by the spectroscopic techniques. The qualitative
identification of the minerals in beach rock samples was carried out by using FT-IR and XRD technique. Among the
minerals identified by these techniques, calcite was the most abundant mineral. The presence of calcite indicates
directly that they are the constituents of the cementation mineral in beach rock samples. The elemental distribution
in the beach rock samples was determined by using instrumental neutron activation analysis (INAA). From the
elemental analysis, calcium was more abundant than other elements and also it exhibited the highest concentration in
almost all locations. This is due to the typical beach rock formation.
From the analysis, the beach rocks may derive the cement from seawater. Seawater is several times supersaturated
with respect to calcite and aragonite and also it is the source of cementing agent calcium carbonate. Many workers
reported that calcium carbonate is the cementing materials for beach rock formation and it supports the statement.
The combined use of mineralogical and multi-elemental analysis is an adequate methodology to identify the source
of cementing material for the beach rock formation. This study demonstrates the feasibility of spectroscopic
techniques for the analysis of beach rock samples and it is proven that these techniques can be used for
environmental matrix.
Acknowledgement
The authors are highly indebted to Dr. P. R.Vasudeva Rao, Director, Chemistry Groups, IGCAR, Kalpakkam,
Tamilnadu, India for fruitful discussions, constructive suggestions, moral support and constant encouragement in
each step of the INAA work.
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